The invention relates to a roll with a rotationally fixed carrier and a roll jacket which is rotatable about the carrier and supported relative to the carrier by at least one support element exerting a supporting force in a pressing plane, the roll jacket being built up of a plurality of several concentric zones of different characteristics, and to the use of the roll for cooling or heating purposes.
Such so-called deflection controlled rolls equipped with support elements of controllable support force and having a multi-layered roll jacket are for example known from DE 35 25 950 and are used for the thermal treatment of webs of material. In this arrangement, the individual layers of the roll jacket have differing physical, and in particular thermal, characteristics.
As a rule, the inner zone of the roll jacket consists of a hard material, for example metal, and the outer zone of a soft material, for example an elastomer such as soft caoutchouc or the like. Such deflection controlled rolls with roll jackets of this known kind are however only conditionally suited for some uses, for example for the thermal treatment of a paper web in a smoothing calender or for the thermal treatment or manufacture of a plastic foil. It is in particular a disadvantage that the outer zone has a poor thermal conductivity so that good thermal dissipation is not guaranteed and the temperature can only be kept inadequately constant during the treatment of the web of material.
The use of deflection controlled rolls for plastic foil pouring plants is for example known from DE-A-33 00 251. In this arrangement the flowable plastic composition is directed between two rolls and is brought to a desired thickness profile during solidification by means of the controllable support force of the support elements of the deflection controlled roll. Such deflection controlled rolls with roll jackets of the known kind are however only poorly suited for certain plastics which exhibit a relatively sudden transition between the flowable and the solid state in a narrow temperature range. On the one hand, with such rapidly solidifying plastics, for example polyethylene, the pressing and thickness control processes must take place at a precisely determined time point at a temperature which is as exact as possible, which is not required to the same degree with thermoplastics with a larger solidification range. On the other hand, rapidly solidifying plastics tend to stick during the solidification process to the customary roll surfaces.